Rate of ingestion by mosquito larvae (Diptera: Culicidae) as a factor in the effectiveness of a bacterial stomach toxin

To study the impact of ingestion rate on the effectiveness of the stomach toxin produced by Bacillus thuringiensis var. israelensis , fourth-instar larvae of Aedes aegypti, Culex quinquefasciatus, Anopheles albimanus , and Anopheles quadrimaculatus were exposed to a series of toxin suspensions at larval densities ranging from 0.15 to 2.4 individuals per ml water. Toxin was dosed as weight per larva; consequently, toxin concentration increased with increasing larval density. The authors conclude that the relative tolerance of Anopheles larvae to suspensions of the bacterial toxin is a result of their low filtration rates. In Cx. quinquefasciatus , toxin effectiveness did not change with larval density, possibly due to feeding inhibition caused by the bacterial agent.